1. Field of the Invention
The present invention is related to an imaging apparatus. More specifically, the present invention is related to an imaging apparatus and a biological data imaging method that irradiates light onto a subject, obtains images based on acoustic signals which are generated accompanying the irradiation of light, emits ultrasonic waves into the subject, and obtains images based on the reflected ultrasonic waves.
2. Description of the Related Art
The ultrasound examination method is known as a method that enables non destructive examination of the states of the interiors of examination targets. Ultrasound examinations employ ultrasound probes which are capable of outputting and detecting ultrasonic waves. When ultrasound probes are placed in contact with examination targets and ultrasonic waves are generated, the ultrasonic waves propagate within the interiors of the examination targets, and are reflected when they reach hard objects. The ultrasound probes detect the reflected acoustic waves, and distances are calculated based on the time for the reflected waves to reach the ultrasound probe, to enable visualization of the interiors of the examination targets as images.
Photoacoustic imaging is also known as a method for imaging the interiors of living organisms by utilizing the photoacoustic effect. Generally, in photoacoustic imaging, pulsed laser beams such as laser pulses are irradiated into the living organisms. Biological tissue that absorbs the energy of the pulsed laser beams generate ultrasonic waves (photoacoustic signals) by volume expansion thereof due to heat. The photoacoustic signals are detected by an ultrasound probe or the like, and the detected signals are analyzed, to enable visualization of the living organisms based on ultrasonic waves.
Japanese Unexamined Patent Publication No. 2005-21380, for example, discloses an apparatus that generates and displays ultrasound images and photoacoustic images. When generating an ultrasound image, the apparatus outputs ultrasonic waves into the interior of an organism from probe elements of an ultrasound probe. Reflected acoustic waves, that is, the reflected ultrasonic waves, are detected by adjacent probe elements of a predetermined number of channels. The detected reflected acoustic waves are phase matched and added, to enable specification of the depth positions within the organism at which the ultrasonic waves were reflected. The output of ultrasonic waves and detection of reflected acoustic waves are repeatedly executed while shifting the probe element corresponding to single channels (single lines), to construct the ultrasound image.
Meanwhile, when generating a photoacoustic image, light from a light source is guided to biological tissue by a waveguide section, and a pulsed laser light beam is irradiated onto the biological tissue. After irradiation of the pulsed laser beam, photoacoustic signals are detected by the adjacent probe elements of a predetermined number of channels of the ultrasound probe in a manner similar to that during generation of the ultrasound image. The detected photoacoustic signals are phase matched and added, to enable specification of the depth positions within the organism at which the photoacoustic signals are generated. The irradiation of the pulsed laser beam and the detection of the photoacoustic waves are repeatedly executed while shifting the probe element corresponding to single channels (single lines), to construct the photoacoustic image.
Here, the phase matching addition process is a common process in both generation of the ultrasound image and generation of the photoacoustic image. In phase matching addition in the two types of image generation, reflected acoustic waves and photoacoustic signals which have been sampled in parallel by respective sampling circuits are input, the input reflected acoustic waves and photoacoustic signals are respectively phase matched and added. Generally, the number of pieces of data (number of channels) capable of being sampled in parallel by sampling circuits is less than the number of probe elements provided on an ultrasound probe. For example, the total number of probe elements of an ultrasound probe is 128, and a sampling circuit is capable of sampling data corresponding to 64 channels in parallel. In this case, data from 64 probe elements are respectively phase matched and added to generate the ultrasound image and the photoacoustic image.
How to set the range of phase matching when generating ultrasound images and photoacoustic images in apparatuses which are capable of generating both types of images had not heretofore been discussed. The present inventors have found that it was not possible to achieve both high resolution ultrasound images and high resolution photoacoustic images in the case that the phase matching range is the same when generating the two types of images.